Whisk together flour, baking powder, and salt in a medium bowl
If using solid fat, rub into flour until the mixture takes on a coarse crumb texture.
Add water (and oil, if using liquid oil) and work with hands until all the water is absorbed and no dry flour is left in the bowl.
Turn out and knead for 1 minute or until smooth. Cover and allow to rest 10 minutes, then divide into 4 equal pieces and shape each into a ball. Cover and rest another 15 minutes.
Preheat cast iron skillet to 500°F.
Press a dough ball into a disc and roll out into an 8-inch round tortilla. Cook on each side until brown spots form on bottom, about 30–60 seconds.
Serve warm, or refrigerate and re-heat in skillet (or wrapped in aluminum foil in oven).
A note on fat/oil: Lard, butter, or vegetable shortening will give the softest texture. Lard is most traditional and imparts a characteristic porky flavor. Butter will result in a buttery-flavored end product. Neutral cooking oil—corn, vegetable, canola, etc—works fine as well, but gives a slightly less soft tortilla.